Cathode coated by partially cyclized polyacrylonitrile with hybrid conductivity for long-lifespan solid-state garnet batteries.

The garnet LiLaZrO solid electrolyte presents promising potential in application of solid-state lithium batteries because of its high ionic conductivity and stability. However, the critical interfacial issues between cathodes and garnet electrolytes severely restrict capacity and cycling stability of solid batteries. In this work, the partially cyclized polyacrylonitrile (cPAN) nanolayer is coated on high-voltage LiNiCoMnO (NCM) cathode particles enabling interface-friendly solid-state garnet batteries. Through controlling cyclized temperature and time, the cyclized part of polyacrylonitrile equipped with delocalized spπ bond presents good capability for electronic transfer, while the residual part not involved in cyclization leaves the coating with certain feature for ionic transfer. In this way, such hybrid-conductivity coating facilitates the transport of both ions and electrons inside the cathode. In addition, the moderate cyclization condition retains the elasticity of polymers, contributing to protection of NCM cathode and suppression of side reactions at NCM/garnet interface during cycling. Therefore, the resultant solid NCM/garnet/Li cell based on the proposed interface engineering strategy delivers a discharge capacity of 176 mAh g with a capacity retention of 82.4 % after 400 cycles. This work puts forwards an attractive strategy to modulate the cathodic interfaces toward solid-state garnet batteries via introducing partially cyclized polyacrylonitrile protective layer with hybrid conductivity.